Search

A combined analytical method of NEXAFS measurement and DFT-calculation was employed for the evaluation of Cs states in clay minerals. The measured Cs M4,5 NEXAFS spectra of Cs halides were analyzed using the DFT-calculations in order to establish the analytical methods. The NEXAFS spectra of the Cs halides were well reproduced by incorporating the core-hole strength. The Cs M4,5 NEXAFS spectrum of the clay minerals was well reproduced by the DFT-calculations including the major transitions and tail structures with the established method. Further evaluation of this spectrum by charge density analysis suggested that these major transitions and the tail structures likely reflect the bonding state and the local environment around the Cs atoms. Comparison of electronic states of Cs in the clay mineral with those in the Cs halides by DFT-calculations has shown that the interaction between Cs and the nearest-neighbor atom is largest in the clay mineral, which differs from those of Cs halides. This happened due to the energy level of Cs-5s and 5p, which was closer to that of O-2s and 2p than the s and p orbitals of other alkali metal and alkali earth metal elements.

The 6-methyl 2-(2-pyridyl)-benzimidazole ligand coordinates with the actinide species in solution, and the complexes exhibit efficient intramolecular energy-transfer processes. It is revealed that sensitized orange-red emission of Cm(III) is readily observed at low concentrations.

Abstract: Coordination of the 6-methyl-2-(2-pyridyl)-benzimidazole ligand with actinide and lanthanide species can produce enhanced emission due to increased efficiency of intramolecular energy transfer to metal centers. A comparison between the curium and terbium systems indicates that the position of the ligand''s triplet state is critical for the enhanced emission. The energy gap between the ligand''s triplet state and the acceptor level in curium is about 1000cm−1, as compared to a ~600cm−1 gap in the terbium system. Due to the larger gap, the back transfer with curium is reduced and the radiative yield is significantly higher. The quantum yield for this “sensitized” emission increases to 6.2%, compared to the 0.26% value attained for the metal centered excitation prior to ligand addition. In the terbium case, the smaller donor/acceptor gap enhances back transfer and the energy transfer is less efficient than with the curium system. [Copyright &y& Elsevier]

The new diamide compound, N,N′-dimethyl-N,N′-diphenylpyridine-2,6-dicarboxyamide (DMDPhPDA), was synthesized and the distribution ratios of lanthanides from 1 to 5 M nitric acid solutions into DMDPhPDA CHCl3 solution were determined. The extraction mechanism of lanthanide with DMDPhPDA was discussed based on the slope analysis of acid and ligand concentration dependencies and the variation of distribution ratio along the lanthanides series. The number of DMDPhPDA molecules in extracted complexes increase from 3 for lighter lanthanides to 4 for heavier lanthanides. From the previous EXAFS study of a complex similar in structure, Ln(III) would form an inner-sphere complex with the two DMDPhPDA molecules and an outer-sphere complex with the third and/or fourth DMDPhPDA molecules in addition to an inner-sphere complex. Nitric acid concentration has more influence on the distribution ratio and the difference of distribution ratio among lanthanides than the ligand concentration. [ABSTRACT FROM AUTHOR]

The local structure of molten GdCl3 and its mixture in LiCl–KCl eutectic was investigated by Gd K-edge extended X-ray absorption fine structure (EXAFS) technique. As the result of curve fitting analysis, the nearest Gd3+–Cl− distance was 2.74±0.02Å with coordination number 6.5±0.3 in the pure melt. On the other hand, those in the 10% GdCl3 mixture melt decreased to 2.70±0.01Å and 6.1±0.3, respectively. These results suggest that octahedral coordination (GdCl6)3− structure is formed and stabilized by mixing with the alkali chlorides. The result was compared with that of YCl3 and LaCl3 in LiCl–KCl eutectic melt. [ABSTRACT FROM AUTHOR]

The in situ measurement technique for a metal/metal-oxide mixture at extra-high temperature above 2000 K has been desired in the field of nuclear safety engineering. In the present study, we succeeded in simultaneous XAFS-XRD measurements of the Zr oxidation [Zr + O → Zr(O) + ZrO 2 ] up to 1952 K and ZrO 2 -Y 2 O 3 reaction from 1952 to 2519 K. The chemical shift during Zr oxidation was observed in the absorption spectra around the Zr K-edge, and the interatomic cation-cation and cation-oxygen distances obtained by the fitting analysis of EXAFS during the Y 2 O 3 -ZrO 2 reaction are explained. Also, the temperature dependency of the anharmonic effect was investigated by comparing the fitted second- and third-order cumulants with the theoretical ones in which the Morse potential was applied as an interatomic potential, giving a good explanation about the local structure dynamics. Finally, the applicability of the developed system to investigation of nuclear fuel materials, such as UO 2 -Zr, is discussed., (open access.)

Adsorption reactions of various cations on clay minerals have different effects on their environmental behaviors depending on the molecular-scale adsorption structure. Some cations form outer-sphere complexes via hydration, while others create inner-sphere complexes through dehydration. This preference dictates their environmental impact. However, the factors controlling these complex formations remain unclear. Furthermore, research on the adsorption preferences of radium (Ra) is lacking. Thus, this study conducted the first EXAFS study of Ra 2+ adsorbed on clay minerals and showed that Ra 2+ forms inner-sphere complexes on vermiculite, which can be surprising because Ra 2+ is a divalent cation and prefers to be hydrated. In order to investigate the factors controlling the complex formations, this study conducted systematic EXAFS measurements and DFT calculations for alkali and alkaline earth metal cations. The results showed the importance of the size-matching effect between the adsorbed cation and the cavity of the tetrahedral sheets and that the complex formation can be estimated by the combination of the ionic radius and hydration enthalpy of the adsorbed cation. Furthermore, this study also analyzed environmental core samples. Their results showed the fixation of Ra 2+ by clay minerals and the controlling factors can effectively predict cation environmental behavior., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Akiko Yamaguchi reports financial support was provided by Japan Society for the Promotion of Science and by Japan Atomic Energy Agency., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Here, we investigated the mechanism underlying the extraction of Se(iv) and Se(vi) from aqueous HCl solutions by N -2-ethylhexyl-bis( N -di-2-ethylhexyl-ethylamide)amine (EHBAA). In addition to examining extraction behavior, we also elucidated structural properties of the dominant Se species in solution. Two types of aqueous HCl solutions were prepared by dissolving a Se IV oxide or a Se VI salt. X-ray absorption near edge structure analyses revealed that Se(vi) was reduced to Se(iv) in 8 M HCl. Using 0.5 M EHBAA, ∼50% of Se(vi) was extracted from 0.5 M HCl. In contrast, Se(iv) was hardly extracted from 0.5 to 5 M HCl; however, at molar concentrations above 5 M, the extraction efficiency of Se(iv) increased drastically, reaching ∼85%. Slope analyses for the distribution ratios of Se(iv) in 8 M HCl and Se(vi) in 0.5 M HCl showed that apparent stoichiometries of Se(iv) or Se(vi) to EHBAA were 1 : 1 and 1 : 2, respectively. Extended X-ray absorption fine structure measurements revealed that the inner-sphere of the Se(iv) and Se(vi) complexes extracted with EHBAA was [SeOCl 2 ] and [SeO 4 ] 2- , respectively. Together, these results indicate that Se(iv) is extracted from 8 M HCl with EHBAA via a solvation-type reaction, whereas Se(vi) is extracted from 0.5 M HCl via an anion-exchange-type reaction., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The solvent extraction of Sr(ii) was carried out using dicyclohexano-18-crown-6 (DCH18C6) and two HFC mixed solvents MS1 and MS2, where MS1 was composed of 30/60 (w/w)% trans -1,2-dichloroethylene/HFC-43 (HFC-43: 1,1,1,2,2,3,4,5,5,5-decafluoropentane) and MS2 was 5/95 (w/w)% heptane/HFC-43. Nitric acid and perfuruoro-3-6-9-trioxaundecane-1,11-dioic acid (H 2 PFTOUD) were used to study the effect of acid on the extraction. The maximum distribution ratio of Sr(ii) ( D Sr ) observed for H 2 PFTOUD conditions was ∼180, and >10 times larger than aqueous nitric acid conditions. The D Sr value was influenced by concentrations of the DCH18C6, Sr(ii), and acid, and by temperature. The composition of extracted complexes was estimated using slope analysis as an Sr(ii)-anion-DCH18C6 ratio of ∼1 : 2 : 1. From the extended X-ray absorption fine structure (EXAFS) measurements of Sr(ii) in the aqueous and organic phases, it is inferred that regardless of the acid used, DCH18C6 coordinates to the first coordination sphere of the Sr(ii) extracted complexes and Sr(ii) is hydrated (complexation with H 2 PFTOUD cannot be distinguished) in the aqueous phase. Thermodynamic data were significantly changed by choice of acid, i.e. , both enthalpy and entropy values were negative for nitric acid conditions, on the other hand, entropy values were large and positive for H 2 PFTOUD conditions. These results have demonstrated that the combination of HFC solvent and crown ether is applicable for metal extraction., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Radium is refocused from the viewpoint of an environmental pollutant and cancer therapy using alpha particles, where it mainly exists as a hydrated ion. We investigated the radium hydration structure and the dynamics of water molecules by extended X-ray absorption fine structure (EXAFS) spectroscopy and ab initio molecular dynamics (AIMD) simulation. The EXAFS experiment showed that the coordination number and average distance between radium ion and the oxygen atoms in the first hydration shell are 9.2 ± 1.9 and 2.87 ± 0.06 Å, respectively. They are consistent with those obtained from the AIMD simulations, 8.4 and 2.88 Å. The AIMD simulations also revealed that the water molecules in the first hydration shell of radium are less structured and more mobile than those of barium, which is an analogous element of radium. Our results indicate that radium can be more labile than barium in terms of interactions with water., Competing Interests: The authors declare no competing interests., (© 2022 The Author(s).)

Liquid-liquid extraction of lanthanide (Ln) ions was investigated using N,N-dioctylthiodiglycolamic acid (DOTDGAA), which is a sulfur donor ligand with an amide group and a carboxyl group connected by a thioether chain. The extraction performance and selectivity of DOTDGAA for Ln ions were compared with those of N,N-dioctyldiglycolamic acid (DODGAA), which is also an oxygen donor ligand with a similar chemical structure, to assess the effect of the soft/hard donor atom on Ln separation. DOTDGAA quantitatively extracted all Ln ions while being selective toward the light and middle Ln ions, in contrast to the selectivity of DODGAA for heavier Ln ions. Slope analysis demonstrated that the Ln 3+ transfer using DOTDGAA proceeded through a proton-exchange reaction, forming a 1:3 complex, Ln(DOTDGAA) 3 . The back-extraction of Ln ions from the extracting phase was successfully achieved under acidic conditions., (© 2022. The Author(s), under exclusive licence to The Japan Society for Analytical Chemistry.)

Precise separation and purification of f-block elements are important and challenging especially for the reduction of nuclear waste and the recycling of rare metals but are practically difficult mainly because of their chemical similarity. A promising way to overcome this difficulty is controlling their oxidation state by nonchemical processes. Here, we show resonance-enhanced multiphoton charge transfer in actinide complexes, which leads to element-specific control of their oxidation states owing to the distinct electronic spectra arising from resonant transitions between f orbitals. We observed oxidation of trivalent americium in nitric acid. In addition, we found that the coordination of nitrates is essential for promoting the oxidation reaction, which is the first finding ever relevant to the primary process of photoexcitation via resonant transitions of f-block elements. The resonance-enhanced photochemical process could be used in the nuclear waste management, as it would facilitate the mutual separation of actinides, such as americium and curium.

Understanding the solution chemistry of Pt(iv) is crucial for the hydrometallurgy of precious metals. To gain such an understanding, the speciation and separation of Pt(iv) complexes in concentrated HNO 3 solutions were investigated via Pt L III edge X-ray absorption fine structure (XAFS) spectroscopy. The XAFS results for concentrated HNO 3 solutions of Na 2 Pt(OH) 6 revealed the dominant presence of Pt polynuclear complexes, wherein the formation of Pt(iv) polynuclear complexes depended on the metal concentration and the Na 2 Pt(OH) 6 dissolution temperature. The dominant species present in a heated nitrate solution of 0.90 g-Pt L -1 and a non-heated nitrate solution of 3.2 g-Pt L -1 were dinuclear Pt(iv) complexes, whereas those in a heated solution of 3.0 g-Pt L -1 were predominantly larger polynuclear complexes, such as, tetra- and hexa-nuclear complexes. The presence of larger Pt(iv) complexes was confirmed via XAFS spectroscopy, wherein the adsorption of Pt(iv) ions from a 10 M HNO 3 solution by a chelating resin functionalised with iminodiacetic acid and a strongly basic anion-exchange resin bearing trimethyl ammonium nitrate was examined. The adsorption of 50 mg L -1 of Pt(iv) by the two resins was tested using aqueous solutions diluted from heated HNO 3 solutions with varying metal concentrations, and also from a non-heated solution. We found that Pt(iv) complexes from heating solutions containing high Pt(iv) concentrations displayed high adsorption percentages. In addition, the selective adsorption of Pt(iv) over Pd(ii), Ag(i), Cu(ii), Ni(ii), and Fe(iii) from a 10 M HNO 3 solution was achieved using a strongly basic anion-exchange resin.

Phenanthroline carboxamide compounds are promising for lanthanide intra-series separation. This paper presents a study on the effect of structure modification of phenanthroline carboxamides on the extraction of the whole lanthanide series. The study consists of theoretical calculations, extraction experiments of the 14 stable lanthanides, and extended X-ray absorption fine structure (EXAFS) analyses of Nd and Dy complexes. Tridentate monocarboxamides and tetradentate dicarboxamides show different trends in series extraction, although both preferentially extract the light lanthanides. The amide substituents, although not directly coordinating the metal ions, were also found to impact the distribution ratio, most probably due to a modification in the internal polarity of the molecules. This latter effect, if extrapolated to other nitrogen-based ligands such as pyridines or triazines, can be used to further fine-tune extractants for a process improvement.

Liquid-liquid extraction for the removal of pertechnetate ( 99 TcO 4 - ) and perrhenate (ReO 4 - ) is reported based on using the tripodal extractant N,N,N',N',N″,N″-hexa-n-octylnitrilotriacetamide (HONTA) composed of three amide groups and a tertiary amine. The extraction behaviors were compared with those using alkyldiamideamines (ADAAM(Oct) and ADAAM(EH)), and the commercial amine-type extractant, trioctylamine (TOA). HONTA quantitatively extracted 99 TcO 4 - and ReO 4 - in the pH range from 1.0 to 2.5 by the co-extraction of protons. The extraction performance of the extractants was improved in the order of HONTA > ADAAM(Oct) > ADAAM(EH) > TOA. 99 TcO 4 - and ReO 4 - in the extracting phase were successfully stripped using neutral aqueous solutions as the receiving phase, and the extraction ability of HONTA was maintained after five repeated uses.

The effective recovery of Rh(III) from mixtures also containing Pd(II) and Pt(IV) is one of the most difficult tasks in platinum group metal refining. Adding 3,3'-diaminobenzidine (DAB) to 7 and 10 M HCl aqueous solutions containing Rh(III), Pd(II), and Pt(IV) chlorido species affords the effective separation of Rh(III) from Pd(II) and Pt(IV) through a process where Rh(III) becomes sequestered into solid phases composed of DAB. The stoichiometry and inner coordination sphere of the metal in Rh-DAB complexes were determined by estimating the Rh(III), H + , and Cl - concentrations in the solid phase and X-ray absorption fine structure measurements to clarify the mechanism of DAB selectivity for Rh(III). These results indicate that the Rh-DAB reaction in a concentrated HCl solution occurs in two steps: (1) the precipitation of DAB trihydrochloride salts, where DAB's amino groups are protonated and (2) anion exchange of the trihydrochloride salts for chloride ions with [RhCl 6 ] 3- , which is the predominant species in a concentrated HCl solution. By contrast, ion-pair complexes with [PdCl 4 ] 2- and [PtCl 6 ] 2- were not observed in DAB phases. The significantly lower affinity of the DAB trihydro cation for [PtCl 6 ] 2- and [PdCl 4 ] 2- than for [RhCl 6 ] 3- in 7 and 10 M HCl solutions accounts for the effective separation of Rh(III) from Pd(II) and Pt(IV).

Current methods for the extraction of rhodium carry the highest carbon footprint and worst pollution metrics of all of the elements used in modern technological applications. Improving upon existing methods is made difficult by the limited understanding of the molecular-level chemistry occurring in extraction processes, particularly in the hydrometallurgical separation step. While many of the precious metals can be separated by solvent extraction, there currently exist no commercial extractants for Rh. This is due to its complicated mixed speciation upon leaching into hydrochloric acid, which gives rise to difficulties in designing effective reagents for solvent extraction. Herein we show that the diamidoamine reagent N- n-hexylbis( N-methyl- N- n-octylethylamide)amine transports Rh(III) from aqueous HCl into an organic phase as the monoaquated dianion [RhCl 5 (H 2 O)] 2- through the formation of an outer-sphere assembly; this assembly has been characterized by experimentation (slope analysis, FT-IR and NMR spectroscopy, EXAFS, SANS, and ESI-MS) and computational modeling. The paper demonstrates the importance of applying a broad range of techniques to obtain a convincing mode of action for the complex processes involved in anion recognition in the solution phase. A consistent and comprehensive understanding of how the ligand operates to achieve Rh(III) selectivity over the competitor anion Cl - has emerged. This knowledge will guide the design of extractants and thus offers promise for improving the sustainability of metal extraction from both traditional mining sources and the recycling of secondary source materials.